Signal error detection in railroad communication system

ABSTRACT

A communication system for a distributed locomotive power/brake control system for a railroad train having a lead locomotive and one or more remote locomotives. Command and status signals are communicated over the system between the lead and remote locomotives. Each communicated message includes an information segment comprising the command or status information, and an error control segment for detecting errors in the information segment. The error control segment further comprises cyclic redundancy code words and parity bits formed according to the horizontal or vertical parity of the information segment and the cyclic redundancy code words.

This invention claims priority to the provisional patent applicationfiled on Oct. 17, 2001 and assigned application No. 60/329,984.

FIELD OF THE INVENTION

This invention relates generally to railroad communication systems, andmore particularly to error detection subsystems operative in conjunctionwith railroad communication systems.

BACKGROUND OF THE INVENTION

Radio communication systems (of voice or data signals) for trains havinga lead unit and one or more remote control units or groups of remotecontrol units are known. This arrangement where the locomotives aredistributed within the train consist is referred to as distributed poweroperation and thus the communication system is referred to as adistributed power communication system. Generally, the one or moreremote units or groups of remote units are controlled by commands fromthe lead unit carried over the communication system. The radiocommunication channel also carries responses by the remote units to thelead unit commands. In addition, certain important alarm conditions inthe remote units and operational parametric data are brought to theattention of the engineer in the lead unit to ensure accurate and safetrain operation.

Since many of the messages communicated between the lead and remoteunits in the moving train relate to proper traction and brakingcommands, they must be reliably and accurately received, even under avariety of changing operational and environmental conditions that affectthe reliability of the communication link. Also, accuracy andreliability are required for signals communicated between the train andvarious land-based sites, such as a dispatching center, a locomotivemonitoring and diagnostic center, personnel in a rail yard or in aloading/unloading facility and wayside equipment.

FIG. 1 schematically illustrates a train 18 and a distributed powercommunication system 10 for carrying control and monitoring signalsbetween one or more remote units 12 and 13 and a lead unit 14 (FIG. 1).In another embodiment, not shown, the function performed by the leadunit 14 is replaced by a control tower where commands are issued(directly of via the lead unit) by a dispatcher to all locomotives inthe train consist. An off-board repeater 26 may be disposed within radiocommunication distance of the train 18 for relaying communicationsignals transmitted between the lead unit 14 and the remote units 12 and13 when direct communication between the lead unit 14 and the remoteunits is hampered, such as while the train 18 is traveling through atunnel. The lead unit 14, the remote units 12 and 13, the off-boardrepeater 26 and the control tower (not shown) are provided with atransceiver 28 (and an antenna 29) for receiving and transmitting thecommunication signals. The lead unit transceiver 28 is associated with alead controller 30 for issuing commands to control the remote units 12and 13 and for responding to incoming signals from the remote units 12and 13. Each of the remote units 12 and 13 and the off-board repeater 26includes a remote controller 32 responsive to a signal from thetransceiver 28 of the lead unit 14 for responding to the lead unitcommands. The controller 32 can also initiate the transmission ofmessages to the lead unit 14 to advise of status information and alarmconditions.

In one embodiment of the existing railroad communication system, thecommunication link is a single half-duplex communication channel with athree KHz bandwidth. Each message transmission comprises a serial bitstream code word, further comprising information bits and errordetecting bits derived from a geometrical error detecting scheme,modulating a carrier signal according to known frequency-shift keyingmodulation techniques. The types, contents and format of the variousmessages carried over the communication system 10 are described indetail in the commonly owned U.S. Pat. Nos. 5,039,038 and 4,582,580,both entitled Railroad Communication System, which are incorporated byreference herein. The system elements and message formats were intendedto provide a secure transmission link for the information signals, witha low probability of accepting a message corrupted during transmission.The system also was intended to offer a low probability of interferencefrom other lead and remote units on the same radio channel and withinradio transmission distance.

The train 18 further includes a plurality of cars 20 that separate thelead unit 14 from the remote units 12 and 13. The cars 20 are coupled bya brake pipe 22 that signals a brake application in response to a dropin brake pipe pressure and a brake release in response to a pressureincrease. The pressure in the brake pipe is controlled by an air brakecontroller 24 in the lead unit 14 and any or all of the remote units 12and 13.

Each message includes information bytes or words and error detectingbits. As is known in the art, the inclusion of error detecting bitsallows the receiver to detect bit errors that can occur duringtransmission over a noisy channel, at the expense of increasing themessage overhead. In a prior art embodiment of the communication system10, the error detecting bits are constructed in a geometrical format ashorizontal and vertical parity bits. Each information byte is checkedfor odd or even parity, and as required an extra bit is added to satisfythe odd or even parity condition. This extra bit is referred to as ahorizontal parity bit. Each message also includes a vertical parity bytethat is generated to create a selectable odd or even parity for eachcolumn in the message, where the columns are formed by juxtaposing thewords or bytes in overlying rows and determining the bit parity in eachcolumn. Once the parity of each column is determined, the verticalparity byte is formed to provide odd or even parity for the column.

An example is shown in FIG. 2 where the individual bits for informationwords A through D are set forth. These bits are merely illustrative andare not intended to represent a complete message carried over thecommunication system 10. Each word has eight information bits, labeled 0through 7. The column labeled “HP” is the horizontal parity bit. In theexample, odd parity is selected and therefore the value in the HP columnis selected to ensure that an odd number of ones appear in each row, orthat each of the bytes has odd parity. The vertical parity isestablished by the word in the “VP” row and in this example is selectedto ensure that an even number of ones appear in each column.

The horizontal and vertical parity bits are employed at the receivingunit of the communication system 10 to determine whether errors occurredin the message as it traversed the channel. Upon receipt of a message bythe lead unit 14 or a remote unit 12 or 13, the associated transceiver28 demodulates the received signal into a baseband binary serial datastream and segregates the data stream into individual bytes. Theapplicable controller 30 or 32 determines the horizontal parity of thedemodulated bytes as they are segregated. To determine the verticalparity, the bytes are arranged into a block form such as illustrated inFIG. 2. (Note that the formation of the code block of FIG. 2 is merelyillustrative. It is not necessary to construct the block as the verticalparity can be determined by buffering individual bits such that bufferedbits can be analyzed as though they were oriented in a column.) If thereceived words have the correct vertical and horizontal parity, thecommand or message represented by the baseband information segment isexecuted. If the parity is incorrect, the receiving unit rejects themessage and a response is not transmitted. If the initiating lead unit(or the tower) does not receive a valid response from each unit to whichthe message was targeted, the message is retransmitted. At the receivingunit the retransmitted message is again demodulated and processedthrough the error detecting steps.

During most communication intervals the train is in motion. Thus thecommunication link can be lost or degraded when man-made or naturalstructures interfere with the communication path between thetransmitting and receiving units as the train traverses the track. Also,the communication signal can be disrupted when the line-of-sight is lostbetween the transmitting and receiving units. Such link disruptions cancause errors in the received message. It has been observed duringoperation of the prior art distributed power communication system asdescribed above, that certain four-bit errors in the received messagemay not be detected. There is also a statistically significantprobability of not detecting errors with more than four erred bits. Iferrors go undetected at the receiving unit, train operational problemsmay arise. For example, if the lead unit 14 transmits a brakeapplication command to the remote units, and the command is corruptedduring transmission, but the corruption created errors in anundetectable error pattern, then the command is interpreted as a validcommand, but a brake application is not made at the remote units 12 and13.

An example of undetected errors that can occur with the prior artgeometrical parity scheme is illustrated in FIG. 3. One class ofundetectable errors cause an even number of errors in an even number ofrows, where the errors occur in the same columns within each row. Forsimplicity, FIG. 3 illustrates only five rows of information words, eachword comprising eight bits, plus a horizontal parity bit (HP) and avertical parity bit (VP). Odd parity was selected. The erred bits arestricken and the value of the erred bit written above the strike mark.An error occurs when a transmitted zero bit is received as a one bit (orvice versa) due to noise and other channel effects. As can be seen bychecking the parity of each row and column after occurrence of theindicated errors, the horizontal and vertical parity bits still indicatefive correct information words, notwithstanding four erred bits. Suchundetected errors can cause serious operational problems as the remoteunits 12 and 13 will not receive the correct command or data astransmitted from the lead unit 14, but are unable to determine that anerror occurred.

Implementation of additional error detection capability to reduce thebit error probability is constrained by the large number of operationallocomotives (lead units 14 and remote units 12 and 13) currentlyutilizing the prior art geometric parity scheme described above and therequirement that all locomotives in a fleet must be interoperable. Theprocess of assembling a train having multiple locomotives so as to havesufficient motive power to meet the train's mission requirements is acomplex one that would be made more difficult by the additional issue oflocomotive communication system interoperability. Thus it is notpossible to reduce the bit error rate by simply upgrading thecommunication system 10 of just isolated, individual locomotives toinclude one of the known more powerful error detecting methods, as thelocomotives operating with the legacy geometric parity scheme would thennot interoperate with the locomotives employing the newer errordetecting scheme. Upgrading all locomotives throughout the entire NorthAmerican railway network over a short period of time is problematic.Such a conversion would be a time-consuming, burdensome and expensivetask in light of the large number of locomotives involved, theirgeographic dispersion and the various railroad company owners.

The problem thus remains to provide an error detecting scheme thatreduces the bit error rate below that provided with the existinggeometric parity scheme, while providing interoperability withcommunication systems employing the existing geometric parity scheme.

BRIEF SUMMARY OF THE INVENTION

To improve the error detecting capabilities of the distributed powercommunication system, the present invention teaches the use ofadditional error detection bits that form part of the information to betransmitted and operable in combination with the existing geometricparity bits schemes. This enables the transmitted word to be decoded bya receiver having additional error detection capability with greateraccuracy and reliability. At the same time, the additional errordetection bits are ignored by a receiving unit that is not equipped toprocess the additional error detection bits. In a preferred embodiment,a cyclic redundancy code polynomial is used to provide the additionalerror detection bits.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features of the invention will be apparent fromthe following more particular description of the invention, asillustrated in the accompanying drawings, in which like referencecharacters refer to the same parts throughout the different figures. Thedrawings are not necessarily to scale, emphasis instead being placedupon illustrating the principles of the invention.

FIG. 1 is block diagram of a railroad train to which the teachings ofthe present invention can be applied;

FIG. 2 is a table illustrating data bits in block format;

FIG. 3 is a data block illustrating undetected errors according to theprior art scheme;

FIG. 4 is a data block illustrating the error detecting bits accordingto the teachings of the present invention;

FIGS. 5 and 6 are block diagrams of an encoder and decoder according tothe teachings of the present invention; and

FIGS. 7 and 8 are flowcharts of the encoding and decoding processesaccording to the teachings of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Before describing in detail the particular railroad communication systemin accordance with the present invention, it should be observed that thepresent invention resides primarily in a novel combination of hardwareelements and method steps related to data error detection. Accordingly,the hardware elements and method steps have been represented byconventional elements in the drawings, showing only those specificdetails that are pertinent to the present invention, so as not toobscure the disclosure with structural details that will be readilyapparent to those skilled in the art having the benefit of thedescription herein.

To improve the error detection capabilities of the communication system10 associated with distributed operation of a railroad train, thegeometric code described above is augmented with a cyclic redundancycheck (CRC) code or a shortened cyclic code.

The substantial improvement in the undetected error performance is dueprimarily to the different and independent schemes for developing theCRC and the geometrical error detecting bits. The two schemes areoptimized to detect different patterns of data errors. The geometricalbits are constructed based on the parity of the message when arranged ina block, and thus certain errors go undetected as illustrated in FIG. 3above. The CRC bits are formed from the remainder produced by dividingthe shifted information bits by a code generator polynomial, such as oneof the code generator polynomials set forth below. Thus the CRC bitsdetect the undetected errors illustrated in FIG. 3. In one embodiment,the combination of the geometric error detecting bits and the CRC bitsimproves the error detecting capabilities by about six orders ofmagnitude over use of the geometric parity bits alone.

Further, the additional error detecting bits generated by the CRC codeare included within the information segment of the message, with thevertical and the horizontal parity bits “wrapped around” both theinformation bits and the CRC bits. FIG. 4 illustrates an exemplarymessage 40, including information bits 41 and CRC bits 42. Horizontalparity bits 43 are formed based on the parity of the rows of informationbits 41 and CRC bits 42. Odd parity is selected for this example.Vertical parity bits 44 (odd parity) are formed based on the columns ofthe information bits 41, the CRC bits 42 and the horizontal parity bits43.

Thus CRC-equipped locomotives utilize both the geometrical parity bitsand the CRC bits to detect message errors. Non-CRC-equipped locomotivescan use only the geometrical parity bits, ignoring the CRC bits assimply extraneous “information” bits that it does not need to process.Although the non-CRC equipped locomotives cannot take advantage of theadditional error detecting capability within the message, they candetect errors based on geometric parity and thus can interoperate withthe CRC-equipped locomotives (and other non-CRC-equipped locomotives).

It is known that cyclic codes are based on a generator polynomial andthat the degree of the polynomial equals the number of check bitsincluded in the bit stream to provide the error detecting function. Oneexemplary generator polynomial appropriate for use with the distributedpower communication system 10 is:g(X)=1+X ² +X ¹⁵ +X ¹⁶.Thus this generator polynomial produces 16 check bits to detect errorsin the information bit stream. When a cyclic code generated according tothe above generator polynomial is annexed to the geometrical codedescribed above, there is a significant improvement in the undetectederror rate performance. In another embodiment a code generatorpolynomial of the formg(X)=1+X ⁵ +X ¹² +X ¹⁶serves as the generator polynomial.

According to one embodiment of the distributed power communicationsystems 10, the message transmitted over the link comprises a 20-32 byteinformation field plus a one-byte vertical parity word. The total codeword is thus 21 to 33 bytes long. Assuming, for example, that a 21 bytecode word is augmented with two cyclic redundancy check (CRC) code bytesof the present invention, then a transmitted code word comprises 18information bytes (144 bits), one horizontal parity bit for eachinformation byte (18 bits), 2 bytes (16 bits) of cyclic redundancy checkbits, and 9 bits of vertical parity. The two CRC bytes check all of theinformation bytes and the horizontal parity bit associated with eachinformation byte. The vertical parity byte checks the CRC bytes and thehorizontal parity bytes. The total message size is 189 bits with 45parity bits. There are 29 geometric parity bits (nine vertical and 18horizontal) plus 16 CRC check bits.

In a situation where the communication system 10 includes oneCRC-capable and one non-CRC-capable locomotive, the CRC-capablelocomotive uses 49 error detecting bits, i.e., the CRC bits, thehorizontal parity bits and the vertical parity bits to perform errordetection. The non-CRC-equipped locomotive uses only the vertical andthe horizontal parity bits (29 bits) and ignores the CRC bits.

In various embodiments, the order in which the two CRC check bytes, thehorizontal parity bits and the vertical parity bits are formed can beinterchanged. Thus according to one embodiment, the CRC check bytes areformed first, followed by the horizontal and then the vertical paritybits. In another embodiment, the CRC check bytes are formed first,followed by the vertical then the horizontal parity bits. In both suchembodiments, the CRC check words are treated as part of the information,with respect to the later formation of the vertical and horizontalparity bits (in either order). Thus this technique is distinguished fromthe conventional error detecting scheme where the error control codewords or bits are appended to the information bits, and treated as aseparate entity for separate processing at the receiving site.

The implementation of the CRC error-checking capabilities into all thedistributed power communication systems operating on today's locomotiveswill take some time to complete. Since for a time there will be bothnon-CRC and CRC distributed power communication systems in operation, itis advisable, as discussed above, to develop an error detecting systemthat is interoperable with both CRC and non-CRC systems. As these legacysystems are upgraded or replaced, CRC error detecting capabilities canbe incorporated. To allow this interoperability, the message formatincludes a bit for indicating whether a locomotive is CRC capable.

When a communication session is initiated, the lead unit 14 indicatesCRC-capability by setting a CRC-designating bit within the message andincluding the CRC code words in the message. If CRC processing isavailable at the receiving unit, that is, either one or both of theremote units 12 and 13, the CRC code words are used to detect errors inthe received message. Also, the designating bit is set in the replymessage and the reply message includes CRC code words generated asdescribed above, i.e., the reply is CRC-capable.

If the receiving unit is not CRC-capable, the CRC designating bit in themessage from the lead unit 12 has no effect and is ignored, the CRC codebytes are ignored as the receiving unit decodes the received message andthe receiving unit replies with a non-CRC reply, that is, where the CRCdesignating bit in the reply message is not set and no CRC code bytesappear in the reply message. The lack of a set bit in the reply messageindicates to the lead unit 14 that the receiving unit is not CRC-capableand thus future messages to that receiving unit are not CRC-encoded.Advantageously, the error detecting scheme of the present inventionwhere the CRC bits are treated as part of the data or information withrespect to the later formation of the vertical and horizontal bits,allows the receiving unit to simply ignore the CRC code words, whilecontinuing to use the horizontal and vertical parity bits for errordetection.

This arrangement permits non-CRC-capable locomotives to receive messagesfrom CRC-capable locomotives and maintain the ability to perform errordetecting on the received message using the horizontal and the verticalparity bits. Thus the non-CRC-capable and the CRC-capable locomotivesare interoperable, with error detection provided by the horizontal andvertical parity bits. Two CRC-capable locomotives can communicate witherror detection provided by both the horizontal and vertical parity bitsand by the CRC bits. The addition of the CRC bits to the message isbackward compatible with messages that lack the CRC code bits.

If the lead unit 14 is not CRC-capable, then the CRC designating bit isnot set in the message and in response the remote units 12 and/or 13reply with a non-CRC reply message. Even if the remote units 12 and/or13 are CRC-capable, CRC operation is suppressed when communicating witha non-CRC lead unit 14.

FIG. 5 illustrates, in block diagram form, an encoder 50 for generatinga message bit stream. Conventionally, the encoder 50 is one element ofthe control unit 30 or 32 in the lead unit 14 or the remote units 12 and13, respectively. The encoder 50 comprises a processing deviceperforming all functions related to the formation of information bits,the CRC bits and the geometric parity bits, or a plurality of processingdevices, each performing one of the listed functions. Further, theprocessing device can comprise a general purpose processing deviceprogrammed to perform the illustrated functions, as well as performingother functions within the control units 30 or 32. Alternatively, aspecial purpose processing device can be employed to provide thedescribed functionality.

With respect to FIG. 5, the processing devices are referred to by theirfunctional attributes. The information bytes are assembled in a buffer52 as they are received from other components (not shown) of the leadunit 14 or the remote units 12 and 13, and input to a CRC code analyzer54 for generating the CRC code bits. A vertical parity bit generator 56receives the information bits and the CRC bits, for generating thevertical parity bits (odd or even) as described above. The resultingbits are input to a horizontal parity bit generator 58 for constructingthe horizontal parity bits (odd or even). The output code word is inputto the transceiver 28 for modulating a carrier that is transmitted tothe receiving unit, that is, either or both of the remote units 12 and13 or the lead unit 14.

Although the horizontal parity bit generator 58 is illustrated as aseparate component of the encoder 50, in one embodiment this function isperformed by hardware within the transceiver 28, e.g., by a universalasynchronous receiver/transmitter (UART) that converts the multipleparallel word bit streams of the message into a single serial bit streamfor carrier modulation within the transceiver 28. During that conversionprocess the UART appends the horizontal parity bit.

In another embodiment, the appending of the horizontal and vertical codewords is reversed. That is, the information bytes and the CRC bytes areformed and a horizontal parity bit (odd or even) for each of these bytesis formed. The information and CRC bytes, together with the respectivehorizontal parity bit for each, are then figuratively arranged into thecode block, as illustrated in matrix and the vertical parity of eachmatrix column is determined, after which the vertical parity bit isappended, as determined by whether odd or even vertical parity isselected.

In any of the various embodiments presented herein the horizontal andvertical parities can be the same or different. That is both can be oddor even parity. Alternatively even parity can be selected for thehorizontal parity with odd vertical parity, or vice versa.

At the receiving site, error checking occurs in a decoder 60 depicted inthe block diagram of FIG. 6. The message is received and demodulated inthe transceiver 28. The received bytes are input to a horizontal parityanalyzer 62 where the horizontal parity of each byte is determined. Thecorrect parity (either odd or even) for the bytes is known in advance.Thus the horizontal parity analyzer 62 determines whether the horizontalparity of each received byte is correct.

Although the horizontal parity analyzer 62 is illustrated as a separatecomponent of the decoder 60, in one embodiment the horizontal parityanalysis process is performed within the UART of the transceiver 28during the process of converting the received serial bit stream to aparallel bit stream of individual bytes.

If the horizontal parity of the bytes is correct, the message is storedin a buffer 64. The individual words are accessed by a vertical parityanalyzer 66 to determine the parity of each column and compare theresult with the known correct vertical parity. If the vertical parity iscorrect, the bytes stored within the buffer 64 are accessed by a CRCcode generator 68 and the CRC bits are generated in response to thereceived message. If the generated CRC bits match the received CRC bits,the received message has a very high probability of being free oferrors. The message is then input to the control unit 30 or 32, asappropriate, for further processing consistent with the contents of themessage.

With respect to the alternative embodiment described above wherein theorder of appending the horizontal and vertical parity bits is reversed(i.e., the horizontal parity bit first followed by the vertical paritybit) the order of parity checking at the receiving unit shouldaccordingly be reversed.

As an alternative to regenerating the CRC check bits using thegenerating polynomial and comparing the resultant CRC check bits withthe received CRC check bits, it is known to determine the syndrome ofthe received check bits, where a non-zero syndrome indicates one or moreerrors in the received message.

As described above, in certain operating situations, the lead unit 12may not be able to communicate directly with one or more of the remoteunits 12 and 13, or vice versa. In this situation a repeater station 26serves to receive and retransmit the message between the transmittingand the sending units. According to one embodiment of the communicationsystem 10, the repeater station 26 sets a predetermined bit in thereceived code word to designate the message as a repeated message, thentransmits the message. Thus the message received at the repeater isdifferent than the message transmitted from the repeater. As a result,the repeater station 26 recalculates the vertical parity word andtransmits the message with the set repeat bit and the recalculatedvertical parity word. At the receiving unit (either the lead unit 14 orthe remote units 12 and 13) the received vertical parity word is checkedfirst. If correct, the receiving unit then resets the repeat bit priorto processing through the CRC code generator 68. This technique ensuresthat the use of the repeater station 26 does not thwart the function ofthe CRC bits.

In certain other operational situations the message is repeated by theremote unit 12 or 13, and a different bit in the message is set. Thereceiving unit handles these repeated messages in the same manner as ifthe message was repeated by the repeater station 26 as described above.

The use of the buffers 52 and 64 may not be required for all embodimentsof the invention as certain parity generating and checking schemes canbe executed “on the fly,” that is, as the data bits are being processed,without the need to store the bits.

FIG. 7 is a flowchart of the error detecting code generating processexecuted at the transmitting unit, that is, either the lead unit 14, oneor more of the remote units 12 and 13 or a repeater unit. After theinformation bits of the message are generated by the appropriatecontroller 30 or 32, at a step 80 the CRC check bits are generated. Thevertical parity bits are generated at a step 82 based on both theinformation bits and the CRC check bits. At a step 84, one horizontalparity bit is generated for each byte, including the information bytes,the CRC check bytes and the vertical parity bytes. A bit stream isformed from the individual bytes and modulates a carrier signal fortransmission over the communication channel 10, as represented by a step86. As described above, the order in which the horizontal and verticalparities are checked and the correct parity bit assigned can be reversedaccording to another embodiment of the invention.

FIG. 8 is a flowchart of the error detection code analysis processcarried out at the receiving unit. The message is demodulated and thebinary bit stream formed from the demodulated signal at a step 90.Either concurrently with or after the bit stream is segregated intoindividual bytes, the horizontal parity is analyzed at a decision step92. If the horizontal parity of one or more of the bytes is incorrect,the transmission is rejected as indicated at a step 94. If thehorizontal parity is correct, processing continues to a decision step 96where the vertical parity bits are checked. If the vertical parity isincorrect processing continues to the step 94. If the vertical parity iscorrect, then the CRC check bits are generated at a decision step 98 andcompared with the received CRC check words. If the decision step 98yields an affirmative answer, the received message is deemed correct andprovided to the controller 30 or 32 for execution. As described above,in another embodiment, the order of the horizontal and vertical paritychecking can be switched.

Although the invention has been described in conjunction with acommunication channel between a lead locomotive and one or more remotelocomotives in a distributed power train, the teachings can be appliedto other communication channels. In particular in another railroadapplication the error coding techniques of the present invention can beapplied to communication between a locomotive and wayside equipment, alocomotive monitoring and diagnostic center and equipment operated bypersonnel working in or around the rail yard.

1. A distributed power railroad communication system for communicatingmessages between lead and remote locomotives in a train and a repeaterstation for distributed power operations of the locomotives in thetrain, the communication system comprising: a message source within oneof the locomotives for providing a message; and a processing device forforming information words of the message in response to the informationprovided by the source, for forming one or more error detection wordshaving contents based on all of the information words in the message,and for forming geometric parity bits in response to the informationwords and the one or more error detection words; wherein a messagecomprises the information words, the error detection words and thegeometric parity bits, and wherein the information words furthercomprise a repeat bit position; at the lead locomotive, a transmitterfor transmitting the message to the repeater station; at the repeaterstation, a transceiver for receiving the message and for forming arepeater message in response thereto, wherein the repeater messagecomprises a predetermined bit in the repeat bit position and repeatergeometric parity bits, wherein the transceiver transmits the repeatermessage to the remote locomotives; at the remote locomotives, a receiverfor receiving the repeater message, and in response to a set repeat bit,resetting a repeat bit prior to generating one or more error detectionwords in response to the information words, for determining whether anerror has occurred in the message.